Braided multifilament sutures are commonly used in surgery because of their excellent flexibility and handling properties compared to monofilament sutures of the same material and diameter. It is known in the art that lubricious coatings may be applied as final coatings to the exterior of some types of braided suture to reduce undesirable surface roughness and the excessive tissue abrasion caused thereby, and to improve desirable characteristics, such as the ease of sliding a knot into place, and to increase the tensile strength of the suture. Nevertheless, the coating should not be so lubricious that it jeopardizes the security of the knot, as determined, for example, by the suture's ability to maintain the first throw of the knot.
The tensile strength of a braided suture is of particular concern because of the risk that the suture may break in the incision or wound under tension. The tensile strength of the suture is particularly low at points where the bends of the knot exert additional stress on the braided filaments, increasing the likelihood that the suture will break at the knot as it is tightened. The final coating itself may have an adverse effect on the tensile strength at these points as it tends to bind the filaments, preventing them from moving relative to each other to relieve the tension exerted therein. When a more lubricious coating (i.e., a coating that promotes movement of the fibers) is used, the knot tensile strength of the suture may be improved, but the additional lubrication may degrade the ability of the suture to hold the first throw of the surgeon's knot. Often, an intentional tradeoff is made to obtain an optimal combination of knot tensile strength and the first throw holding characteristic of the suture.
European Patent Publication No. EP 0 908 142 (owned by Ethicon, Inc., Somerville, N.J.), the disclosure of which is incorporated by reference herein, discloses a process for improving the knot tensile strength of a braided suture by tank-coating the surface of the suture with a co-polymer after performing a scouring step (i.e., scouring the suture in an organic solvent), and then heating the suture so that the co-polymer is redistributed among the braided filaments. However, this publication does not address the issue of knot security or disclose the application of a final coat to the suture.
In the foregoing circumstances, there remains a need for a process that will significantly increase the knot tensile strength of a braided suture while preserving the ability of the suture to accept a final coat with the resulting improvement in its desirable properties, especially its first throw holding characteristic.